1. Field of the Invention
The present invention generally relates to improvements in closure mechanisms for gravity discharge openings for grain or commodity type hoppers such as those incorporated in commodity trailers or similar vehicles such as railroad hopper cars. More specifically, the present invention is applicable to hoppers which include downwardly and inwardly sloping bottom panels connected with a vertical peripheral frame member defining a generally rectangular discharge opening.
2. Description of the Related Art
Storage hoppers for various types of granular material and such are well known with such hoppers normally being provided with inwardly sloping bottom wall surfaces terminating in a manner to define a discharge opening. Such hoppers carry a wide range of products including cereal grains, crushed rock, coal, processed or ground grains for feeds, granular fertilizers, dried and processed byproducts from industry, salt, sand, and the like. The trailer typically has two hoppers that funnel the load through the discharge opening for self unloading by the force of gravity, and the opening is closed by a trap. The trap includes a frame attached to the bottom of the hopper and a closure door to retain the commodity within the hopper when shut and release the commodity from the hopper when open.
Door Closure devices are used to selectively open and close the discharge opening of the hopper to enable gravity discharge of the material. Various structures have been provided to form effective closures for the discharge openings including hinged doors and sliding doors. The hoppers could be mounted on various types of vehicles including hoppers especially adapted for use on grain or commodity trailers to enable bulk quantities of material to be transported to a desired site. The following U.S. patents relate to this field of endeavor: U.S. Pat. Nos. 2,544,117; 2,690,352; 2,859,888; 3,958,515; 3,997,089; and 4,193,159.
While these patents disclose various types of closure gates or doors which can reciprocate or pivot, the prior patents do not disclose an inclined door carried by rollers on a frame assembly and reciprocated in horizontal directions by flexible straps through rotation of a single shaft for reducing friction and the effort required for opening and closing the hopper discharge opening.
Typically the trap for opening and closing the discharge opening of the hopper includes a frame to support the mechanical components of the door and a opening and closing mechanism, all of which are located underneath the hopper. The trap frame supports the door and guides the door in horizontal motion. The opening mechanism usually includes a shaft with components to convert rotary motion of the shaft to linear motion of the door by means such as a pinion gear on the shaft and a rack gear secured to the bottom of the door. The frame guides the door in a direction aligned with the trailer. The shaft is usually connected to a universal joint which is in turn connected to a crank shaft supported at the side of the trailer by bearings and configured to permit a user to turn the crank at a convenient height and thereby move the door.
The discharge openings can be quite large, such as in the range upwards of 33".times.43", to permit increased discharge, but such openings require commensurately larger doors. Most doors are supported at their side edges by a ledge on each lateral side of the frame with a plastic wear strip applied therebetween on either the ledge or the door edge. Steel rollers have also been employed between the ledge and door edge in the prior art to reduce friction. The larger doors can require considerable forces during an opening operation of the door, and such traps usually require and include a gearbox reducer on the opening shaft to reduce the torque required at the crank and facilitate operation. The gearbox reducer, however, is typically heavy and burdensome and can require relatively expensive and time consuming maintenance. In addition, the opening mechanism components are typically located below the trap door which detrimentally decreases ground clearance for the trailer which is especially critical over high grade railroad crossings. Cable systems have also been used with the cable wrapping around the shaft, but cables are prone to rust and stiffen, which will increase the opening effort required.
It is, therefore, desirable to reduce frictional forces encountered during the opening operation to decrease the effort required while maintaining optimal ground clearance for the trailer or like vehicle.